Wireshark-bugs: [Wireshark-bugs] [Bug 2221] New: TCP Retransmit packets identified incorrectly
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From: bugzilla-daemon@xxxxxxxxxxxxx
Date: Fri, 25 Jan 2008 15:04:53 +0000 (GMT)
http://bugs.wireshark.org/bugzilla/show_bug.cgi?id=2221

           Summary: TCP Retransmit packets identified incorrectly
           Product: Wireshark
           Version: 0.99.8
          Platform: PC
        OS/Version: Windows XP
            Status: NEW
          Severity: Major
          Priority: Medium
         Component: Wireshark
        AssignedTo: wireshark-bugs@xxxxxxxxxxxxx
        ReportedBy: gmorris@xxxxxxxxxx


Created an attachment (id=1410)
 --> (http://bugs.wireshark.org/bugzilla/attachment.cgi?id=1410)
Packet trace showing the restransmit packets

Build Information:
Version 0.99.8 (SVN Rev unknown)

Copyright 1998-2008 Gerald Combs <gerald@xxxxxxxxxxxxx> and contributors.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Compiled with GTK+ 2.12.5, with GLib 2.14.5, with WinPcap (version unknown),
with libz 1.2.3, with libpcre 6.4, with SMI 0.4.5, with ADNS, with Lua 5.1,
with
GnuTLS 1.6.1, with Gcrypt 1.2.3, with MIT Kerberos, with PortAudio PortAudio
V19-devel, with AirPcap.

Running on Windows XP Service Pack 2, build 2600, with WinPcap version 4.0.2
(packet.dll version 4.0.0.1040), based on libpcap version 0.9.5, without
AirPcap.
Tested with 0.99.7, 0.99.8, and current SVN... Below if from my current SVN
build.


Built using Microsoft Visual C++ 6.0

Wireshark is Open Source Software released under the GNU General Public
License.

Check the man page and http://www.wireshark.org for more information.
--
In the attached packet trace you will see packet 24 indicates that it is a
duplicate ack to packet 21... But how is this true?

Packet 24 details:
Source port: 25222 (25222)
Destination port: 1028 (1028)
Sequence number: 3353540004
Acknowledgement number: 1101552344

Packet 21 details:
Source port: 25222 (25222)
Destination port: 1028 (1028)
Sequence number: 3353539541
Next sequence number: 3353540004
Acknowledgement number: 1101552344

It appears to me that the checking is being performed on the next sequence
number and not the current sequence number. I could try and modify the TCP
dissector but thought that this should be really looked at by the developer
that is currently making the code changes.


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